Re: [PATCH v3 6/8] reset: make sparse-aware (except --mixed)

From: Victoria Dye <vdye@github.com>
Date: Oct 11, 2021, 15:55 UTC
Message-ID: <4a002488-09ba-efed-ac70-c0ec16d7dbe2@github.com>
In-Reply-To: <xmqqlf30edvf.fsf@gitster.g>

Junio C Hamano wrote:

Show 11 quoted lines

> For most callers of prime_cache_tree(), like the ones in "git
> read-tree" and "git reset", it is immediately obvious that we just
> read from the same tree, and we should have everything from the tree
> and nothing else in the resulting index, so it is clear that the
> prime_cache_tree() call is recreating the same cache-tree
> information that we already should have computed ourselves, and
> these calls can go (or if "prime" is still cheaper than "update",
> these callers can pass an option to tell unpack_trees() to skip the
> cache_tree_update() call, because they will call "prime" immediately
> after).
>

After some basic performance testing of `git reset [--hard]`, it's not clear whether `cache_tree_update` is definitively faster or slower than `prime_cache_tree`; more conclusive results would indicate which of the two could be skipped. I'd like to defer this to a future patch (tracking it with an internal issue so I don't forget) where I can perform a more thorough analysis across all of the commands currently using `prime_cache_tree` and update its usage accordingly.